1. Field of the Invention
The present invention relates to an optical disk apparatus, and more particularly, to an optical disk apparatus capable of determining the type of an optical disk.
2. Prior Art
A plurality of types of optical disks, such as a CD-ROM, a CD-R, and a CD-RW, are already on the market. Standards define the reflectivity of an optical disk, such as the reflectivity of a CD-ROM or CD-R as 70% or more and the reflectivity of a CD-RW as 30% or less. An optical disk apparatus which is loaded with an arbitrary optical disk must determine the type of an optical disk loaded and record/reproduce data by means of adjusting a gain and a rotational speed in accordance with the type of the optical disk that has been loaded.
Usually, the amount of light reflected from the optical disk is detected, and the type of the optical disk is determined in accordance with the amount of reflected light. For instance, the amount of light reflected from the optical disk is compared with a threshold value while focus is being attained. If the amount of reflected light is higher than the threshold value, the optical disk is determined to be a CD-ROM. If the amount of reflected light is lower than the threshold value, the optical disk is determined to be a CD-RW.
FIG. 9 shows the configuration of an optical disk apparatus equipped with discrimination function. An optical disk 202 is rotationally driven by a spindle motor 200, and reflected light is received by a pickup 204 located opposite the optical disk 202, whereupon the light is output as an RF signal 206. The RF signal 206 is output to a demodulator, where data are demodulated, and to a terminal of a comparator 208 as well. A reference voltage Vref is supplied to another terminal of the comparator 208, and a comparison result is output to a discriminator 212 as a discrimination signal 210. When focus remains attained, the discriminator 212 checks the discrimination signal 210, thereby determining whether or not the optical disk 202 is an R-LD or an LD. For further information, please refer to Japanese Patent Laid-Open Publication No. Hei 6-267181.
However, under present circumstances, optical disks are supplied from a plurality of manufacturers, and optical disks whose reflectivities fail to meet specifications are circulated in the market. For instance, CD-ROMs include CD-ROMs having a reflectivity on the order of 60% as well as standard CD-ROMs having a reflectivity of 70% or higher. In the prior art, the type of an optical disk is determined by means of a mere reflectivity. Therefore, there arises a problem of a CD-ROM having a reflectivity of 60% being erroneously determined to be a CD-RW.
If a CD-ROM is erroneously determined to be a CD-RW, an RF amplification gain and a servo gain of a reproduction system are set to those for a CD-RW. When data are read from the CD-ROM, a servo signal becomes saturated, thereby resulting in anomalous operation of the optical disk apparatus.
If the optical disk has been erroneously determined to be a CD-RW, the rotational speed will sometimes be controlled to a low speed, thereby raising a problem of a failure to reproduce data at a rotational speed unique to a CD-ROM.
According to the prior art, the type of an optical disk is determined after attainment of focus has been ascertained, and hence processing for detecting a focused state and discriminating an optical disk is required.